An algorithm for 353 odor detection thresholds in humans

One hundred and ninety three odor detection thresholds, ODTs, obtained by Nagata using the Japanese triangular bag method can be correlated as log (1/ODT) by a linear equation with R(2) = 0.748 and a standard deviation, SD, of 0.830 log units; the latter may be compared with our estimate of 0.66 log units for the self-consistency of Nagata's data. Aldehydes, acids, unsaturated esters, and mercaptans were included in the equation through indicator variables that took into account the higher potency of these compounds. The ODTs obtained by Cometto-Muñiz and Cain, by Cometto-Muñiz and Abraham, and by Hellman and Small could be put on the same scale as those of Nagata to yield a linear equation for 353 ODTs with R(2) = 0.759 and SD = 0.819 log units. The compound descriptors are available for several thousand compounds, and can be calculated from structure, so that further ODT values on the Nagata scale can be predicted for a host of volatile or semivolatile compounds.

Ventilation rates and health: multidisciplinary review of the scientific literature

The scientific literature through 2005 on the effects of ventilation rates on health in indoor environments has been reviewed by a multidisciplinary group. The group judged 27 papers published in peer-reviewed scientific journals as providing sufficient information on both ventilation rates and health effects to inform the relationship. Consistency was found across multiple investigations and different epidemiologic designs for different populations. Multiple health endpoints show similar relationships with ventilation rate. There is biological plausibility for an association of health outcomes with ventilation rates, although the literature does not provide clear evidence on particular agent(s) for the effects. Higher ventilation rates in offices, up to about 25 l/s per person, are associated with reduced prevalence of sick building syndrome (SBS) symptoms. The limited available data suggest that inflammation, respiratory infections, asthma symptoms and short-term sick leave increase with lower ventilation rates. Home ventilation rates above 0.5 air changes per hour (h(-1)) have been associated with a reduced risk of allergic manifestations among children in a Nordic climate. The need remains for more studies of the relationship between ventilation rates and health, especially in diverse climates, in locations with polluted outdoor air and in buildings other than offices.

PRACTICAL IMPLICATIONS

Ventilation with outdoor air plays an important role influencing human exposures to indoor pollutants. This review and assessment indicates that increasing ventilation rates above currently adopted standards and guidelines should result in reduced prevalence of negative health outcomes. Building operators and designers should avoid low ventilation rates unless alternative effective measures, such as source control or air cleaning, are employed to limit indoor pollutant levels.

Making scents: dynamic olfactometry for threshold measurement

Data on human odor thresholds show disparities huge enough to marginalize olfactory psychophysics and delegitimize importation of its data into other areas. Variation of orders of magnitude from study to study, much of it systematic, threatens meaningful comparisons with animal species, comparison between in vivo with in vitro studies, the search for molecular determinants of potency, and use of olfactory information for environmental or public health policy. On the premise that good experimental results will flow from use of good tools, this report describes a vapor delivery system and its peripherals that instantiate good tools. The vapor delivery device 8 (VDD8) provides flexibility in range of delivered concentrations, offers definable stability of delivery, accommodates solvent-free delivery below a part per trillion, gives a realistic interface with subjects, has accessible and replaceable components, and adapts to a variety of psychophysical methodologies. The device serves most often for measurement of absolute sensitivity, where its design encourages collection of thousands of judgments per day from subjects tested simultaneously. The results have shown humans to be more sensitive and less variable than has previous testing. The VDD8 can also serve for measurement of differential sensitivity, discrimination of quality, and perception of mixtures and masking. The exposition seeks to transmit general lessons while it proffers some specifics of design to reproduce features of the device in a new or existing system. The principles can apply to devices for animal testing.

The biological and toxicological activity of gases and vapors

A large amount of data on the biological and toxicological activity of gases and vapors has been collected from the literature. Processes include sensory irritation thresholds, the Alarie mouse test, inhalation anesthesia, etc. It is shown that a single equation using only five descriptors (properties of the gases and vapors) plus a set of indicator variables for the given processes can correlate 643 biological and non-lethal toxicological activities of 'non-reactive' compounds with a standard deviation of 0.36 log unit. The equation is scaled to sensory irritation thresholds obtained by the procedure of Cometto-Muñiz, and Cain provides a general equation for the prediction of sensory irritation thresholds in man. It is suggested that differences in biological/toxicological activity arise primarily from transport from the gas phase to a receptor phase or area, except for odor detection thresholds where interaction with a receptor(s) is important.

Concentration-detection functions for the odor of homologous n-acetate esters

Using air-dilution olfactometry, we measured concentration-response functions for the odor detection of the homologous esters ethyl, butyl, hexyl, and octyl acetate. Stimuli were delivered by means of an 8-station vapor delivery device (VDD-8) specifically designed to capture odor detection performance by humans under environmentally realistic conditions. Groups of 16-17 (half female) normosmic (i.e., having a normal olfaction) non-smokers (ages 18-38) were tested intensively. The method involved a three-alternative forced-choice procedure against carbon-filtered air, with an ascending concentration approach. Delivered concentrations were confirmed by gas chromatography before and during actual testing. A sigmoid (logistic) model provided an excellent fit to the odor detection functions both at the group and individual levels. Odor detection thresholds (ODTs) (defined as the half-way point between chance and perfect detection) decreased from ethyl (245 ppb by volume), to butyl (4.3 ppb), to hexyl acetate (2.9 ppb), and increased for octyl acetate (20 ppb). Interindividual threshold variability was near one and always below two orders of magnitude. The steepness of the functions increased slightly but significantly with carbon chain length. The outcome showed that the present thresholds lie at the very low end of those previously reported, but share with them a similar relative trend across n-acetates. On this basis, we suggest that a recent quantitative structure-activity relationship (QSAR) for ODTs can be applied to these and additional optimized data, and used to describe and predict not just ODTs but the complete underlying psychometric odor functions.

Olfactory detection of ozone and D-limonene: reactants in indoor spaces

Young adult subjects who occupied a well-ventilated space with low background of level of ozone achieved via carbon-filtration could detect ozone odor at 7 ppb, lower than expected from archival compilations. The outcome was not inconsistent, however, with some observations of recognition, beyond mere detection, at about 15-20 ppb. Individual differences in sensitivity lay at or just below an order of magnitude, rare in olfactory testing and indicative of precision. In a study of d-limonene, subjects again showed high sensitivity and small individual differences. The subjects could detect the odor at 8 and 15 ppb, depending upon whether they occupied a space with or without carbon filtration, respectively. The results argue for use of carbon filtration to measure sensitivity most stringently, although absence of filtration seems not to incur a large penalty. The protocol used here, with collection of hundreds of judgments in a day, yet with little net exposure of the subject to odorant; with verifiably stable delivery; and with analytical confirmation of level should reduce tolerance for outcomes of large differences among subjects and among studies.

PRACTICAL IMPLICATIONS

Humans manifested much higher sensitivity to ozone and D-limonene than commonly thought, a pattern revealing itself more broadly in olfactory studies as testing improves and analytical confirmation of delivery becomes more common. Published databases, with errors of +/-1000%, often badly underestimate sensitivity and can thereby encourage use of higher concentrations of compounds, particularly VOCs, than relevant in studies of reactive indoor chemistry.

Chemesthetic responses to airborne mineral dusts: boric acid compared to alkaline materials

OBJECTIVES

(1) To assess the relation between occupationally relevant exposures to dust of boric acid and magnitude of feel in the eye, nose, and throat during activity (pedaling) equal to light industrial work. (2) To compare feel from the dust of boric acid with that of the alkaline dusts calcium oxide and sodium tetraborate pentahydrate (sodium borate). (3) To chart how magnitude of feel changes with time in exposures up to 3/4 h.

METHODS

Twelve subjects, six males and six females, participated in duplicate sessions of exposure to 2.5, 5, and 10 mg m(-3) of boric acid, 10 mg m(-3) of sodium borate, 2.5 mg m(-3) of calcium oxide presented as calcium oxide alone or diluted with hydrated calcium sulfate, and 0 mg m(-3) (blank). Exposures occurred in a plastic dome suspended over the head and closed around the neck with rubber dam. Measurements pre- and post-exposure included nasal secretion and nasal resistance. Measurements during exposure included rated magnitude of feel in the eye, nose, and throat, and respiration (Respitrace System). Six concentrations of carbon dioxide ranging from just below detectable to sharply stinging gave subjects references for their ratings.

RESULTS

In general, feel increased for periods up to half an hour, then either declined or held at a plateau. Each material had a temporal signature. The nose led with the highest feel, followed by the throat, then the eyes. This hierarchy proved weakest for boric acid; at one level of exposure, magnitude in the throat overtook that in the nose. Accompanying measures implied that change of feel with time occurred neither because of an increase in dilution of the dissolved dusts in newly secreted mucus nor an increase of consequence in nasal resistance. Most likely, sensory adaptation determined the change. Boric acid of 10 mg m(-3) fell slightly and insignificantly below 10 mg m(-3) sodium borate in feel. Boric acid, though, showed a relatively flat dose-response relationship, i.e., a change in level caused little change in feel.

CONCLUSIONS

The time-constant for feel from dusts lies on the order of tens of minutes. A flat concentration-response function for boric acid and a notable response from the throat suggests that perceived dryness, not mediated by acidity but perhaps by osmotic pressure, may account for the feel evoked at levels of exposure at or below 10 mg m(-3). More acidic dusts that could actually change nasal pH may trigger sensations differently.

A quantitative structure activity analysis on the relative sensitivity of the olfactory and the nasal trigeminal chemosensory systems

We have applied a quantitative structure-activity relationship (QSAR) approach to analyze the chemical parameters that determine the relative sensitivity of olfaction and nasal chemesthesis to a common set of volatile organic compounds (VOCs). We used previously reported data on odor detection thresholds (ODTs) and nasal pungency thresholds (NPTs) from 64 VOCs belonging to 7 chemical series (acetate esters, carboxylic acids, alcohols, aliphatic aldehydes, alkylbenzenes, ketones, and terpenes). The analysis tested whether NPTs could be used to separate out "selective" chemosensory effects (i.e., those resting on the transfer of VOCs from the gas phase to the receptor phase) from "specific" chemosensory effects in ODTs. Previous work showed that selective effects overwhelmingly dominate chemesthetic potency whereas both selective and specific effects control olfactory potency. We conclude that it is indeed possible to use NPTs to separate out selective from specific effects in ODTs. Among the series studied, aldehydes and acids, except for formic acid, show clear specific effects in their olfactory potency. Furthermore, for VOCs whose odor potency rests mainly on selective effects, we have developed a QSAR equation that can predict their ODTs based on their NPTs.

Concentration-detection functions for eye irritation evoked by homologous n-alcohols and acetates approaching a cut-off point

We measured the concentration-detection (i.e., psychometric) functions for the eye irritation evoked by three homologous n-alcohols (1-nonanol, 1-decanol and 1-undecanol) and two homologous acetates (nonyl and decyl acetate). A vapor delivery device based on a dynamic dilution of stimuli in nitrogen served to present various concentrations of each compound, including the undiluted vapor, to the subjects (n >or= 26). Delivered concentrations were quantified by gas chromatography. Detection probability (P) was assessed via a three-alternative, forced-choice procedure and quantified on a scale ranging from P = 0.0 (chance detection) to P = 1.0 (perfect detection). Flow rate to the eye equaled 2.5 l/min and time of exposure was 6 s. The functions for 1-undecanol and decyl acetate plateaued at P approximately 0.5 and P approximately 0.25, respectively, such that further increases in concentration failed to increase detection notably. Thus, both series reached a break point, or cut-off, in the detection of ocular irritation. The present outcome provides additional evidence that the cut-off does not rest on the low vapor concentration of the homolog but, more likely, on the homolog exceeding a critical molecular dimension(s), which prevents it from interacting effectively with the appropriate receptors.

Odor and chemesthesis from exposures to glutaraldehyde vapor

OBJECTIVES

Assessment of olfactory and chemesthetic sensitivity (feel, sensory irritation) to vapor of glutaraldehyde in young adult females. For chemesthetic sensitivity, assessment included the variable of duration, with focus on whether concentrations initially too low to evoke feel in the eye or upper airway might do so in exposures up to 15 min.

METHODS

Experiment 1 probed sensitivity with forced-choice testing of detection over ranges of concentrations appropriate to three endpoints: odor, feel in the eye, and feel in the nose. A subject participated in hours of testing per endpoint to yield enough data to erect a psychometric (concentration-response) function. Exposure in Experiment 1 entailed use of a vapor-delivery system that stimulated sites of interest separately. Exposure in Experiment 2 occurred in the ambient environment of a chamber, with the sites stimulated simultaneously. In that case, subjects rated confidence by the minute that they felt the presence of vapor in the eyes, nose, and throat during exposures of 15 minutes to 35, 50, 75, and 100 ppb, a blank, and an odor control of mild heptane.

RESULTS

In Experiment 1, the typical subject achieved 50% detection (threshold) of odor at 0.3 ppb. The typical subject achieved 50% detection of feel in the eye and nose at 390 and 470 ppb, respectively. Psychometric functions for feel showed much sharper dependence on concentration than those for odor. In Experiment 2, confidence in detection of feel migrated progressively away from no-with certainty toward the zone of uncertainty, with bigger change when the exposures contained any glutaraldehyde. The ratings of confidence failed, however, to show distinguish among these concentrations.

CONCLUSIONS

Glutaraldehyde has much higher odor potency than previously thought. Its green-apple odor should signal presence of the vapor at levels more than a 100-fold below any that might evoke sensory irritation in brief exposures. Exposures that start decidedly below irritating (100 ppb and below) seem unlikely to turn irritating over time. Although the effects from these concentrations differentiated themselves from those of air and an odor control, they exhibited none of the concentration dependence seen for sensations of feel. They seemed likely driven by the penetrating odor of glutaraldehyde.

Chemesthesis from volatile organic compounds: Psychophysical and neural responses

In Experiment 1, subjects sought to localize the nostril stimulated, left or right, in tests with nine esters (acetates, propionates, and butyrates) at concentrations meant to trigger chemesthesis (pungency, irritation). The task produced psychometric functions for chemesthetic detection unconfounded by olfactory sensations. The functions indicated a sharp transition from no detection to perfect detection, rather uniform across the esters, which themselves varied in potency by two log units. The correlation between the thresholds for the eight materials that yielded thresholds and predictions from a published linear free energy relationship (LFER) equaled 0.99. In Experiment 2, amplitude of the negative mucosal potential (NMP) was recorded from the septum. The resulting functions also increased with concentration sharply. Against a criterion amplitude of the NMP, thresholds measured in the first experiment (and predictions from the LFER) correlated 0.99. The NMP seems to offer an adequate objective measure of sensory irritation. The LFER, although effective predictively, could stand to have a parameter to anticipate that molecules beyond a certain size fail to trigger irritation. In the present case, a cut-off of chemesthetic potency occurred between butyl butyrate and hexyl butyrate for the group of subjects, with some variation of the boundary among individuals.

Chemical Boundaries for Detection of Eye Irritation in Humans from Homologous Vapors

In a series of experiments, we looked at a "cutoff" effect for the detection of eye irritation from neat vapors of homologous n-alkylbenzenes and 2-ketones. Stimuli comprised pentyl, hexyl, and heptyl benzene, 2-dodecanone, and 2-tridecanone, presented to each eye at 4 and 8 l/min for 6 sec, using a three-alternative forced-choice procedure against blanks. Detection probability corrected for chance (i.e., detectability) decreased with carbon chain length such that heptyl benzene and 2-tridecanone were virtually undetectable, irrespective of flow rate to the eye. Heating both stimuli sources to 37 degrees C (body temperature) from 23 degrees C (room temperature) increased vapor concentration by 5.0 and 6.9 times, respectively, for heptyl benzene and 2-tridecanone. Still, both chemicals failed to show increased detection for 13 of the 21 participants. In addition, plots of experimentally measured and calculated eye irritation thresholds as a function of carbon chain length for each series indicated that, based on the trend, the concentration of the two cutoff homologs at 37 degrees C should have been high enough to allow detection. Taken together, the results suggest that these cutoffs rest on limitations related to the dimension of the molecules rather than on limitations related to their vapor concentration. For example, the stimulus molecule could exceed the size that allows it to fit into the receptor pocket of a receptive protein. Plots of calculated molecular dimensions across homologous alkylbenzenes, from ethyl to dodecylbenzene, and across 2-ketones, from 2-octanone to 2-octadecanone, provided additional support to the above conclusion.

Odor and chemesthesis from brief exposures to TXIB

An experiment explored ability of subjects to detect vapors of the plasticizer TXIB (2,2,4-trimethyl-1,3-pentanediol diisobutyrate) and ethanol via olfaction and via ocular and nasal chemesthesis, i.e. chemically stimulated feel. Testing, tailored to the sensitivity of each subject, produced psychometric functions for individuals. Olfactory detection of TXIB began at concentrations below 1 ppb (v/v), with 50% correct detection at 1.2 ppb. (Comparable detection for ethanol occurred almost two orders of magnitude higher.) Chemesthetic detection of TXIB began at about 500 ppb, with 50% correct detection at 2.1 ppm for the eye and 4.6 ppm for the nose, both close to saturated vapor concentration. (Comparable detection for ethanol occurred essentially three orders of magnitude higher.) Suggestions that TXIB plays a role in generation of irritative symptoms at concentrations in the range of parts-per-billion need to reckon with a conservatively estimated 200-fold gap between the levels putatively 'responsible' for the symptoms and those even minimally detectable via chemesthesis. Neither the variable of exposure duration nor that of mixing offers a likely explanation. Inclusion of ethanol in the study allowed comparisons pertinent to issues of variability in human chemoreception. An interpretation of the psychometric functions for individuals across materials and perceptual continua led to the conclusion that use of concentration as the metric of detection in olfaction inflates individual differences.

PRACTICAL IMPLICATIONS

This study indicated that the plasticizer TXIB could contribute odor at concentrations in the range of parts-per-billion, but could hardly contribute sensory irritation per se, as alleged in reports of some field studies where TXIB has existed amongst many other organic compounds.

Molecular restrictions for human eye irritation by chemical vapors

Previous research showed a cut-off along homologous volatile organic compounds (VOCs) in their ability to produce acute human mucosal irritation. The present study sought to specify the particular cut-off homolog for sensory eye irritation in an acetate and n-alcohol series. A 1900-ml glass vessel system and a three-alternative forced-choice procedure served to test nonyl, decyl, and dodecyl acetate, and 1-nonanol, 1-decanol, and 1-undecanol. Flowrate to the eye ranged from 2 to 8 L/min and time of exposure from 3 to 24 s. Decyl acetate and 1-undecanol were the shortest homologs that failed to produce eye irritation under all conditions, producing a cut-off effect. Increasing the vapor concentration of decyl acetate and 1-undecanol by 3 and 8 times, respectively, via heating them to 37 degrees C made either or both VOCs detectable to only half of the 12 subjects tested, even though the higher vapor concentration was well above a predicted eye irritation threshold. When eye irritation thresholds for homologous acetates and n-alcohols were plotted as a function of the longest unfolded length of the molecule, the values for decyl acetate and 1-undecanol fell within a restricted range of 18 to 19 A. The outcome suggests that the basis for the cut-off is biological, that is, the molecule lacks a key size or structure to trigger transduction, rather than physical, that is, the vapor concentration is too low to precipitate detection.

Determinants for nasal trigeminal detection of volatile organic compounds

We explored the influence of methodological and chemical parameters on the detection of nasal chemesthesis (i.e., trigeminal stimulation) evoked by volatile organic compounds (VOCs). To avoid odor biases, chemesthesis was probed via nasal pungency detection in anosmics and via nasal localization (i.e., lateralization) in normosmics, in both cases using forced-choice procedures. In the experiments with anosmics, 12 neat VOCs were selected based on previous reports of lack of chemesthetic response. Although none of the VOCs reached 100% detection, detectability and confidence of detection were higher when using a glass vessel system adapted with nosepieces to fit the nostrils tightly than when using wide-mouth glass jars. Half the stimuli were detected well above chance and half were not. When the latter were tested again after being heated to 37 degrees C, that is, body temperature (from room temperature, 23 degrees C), to increase their vapor concentration, only one, octane, significantly increased its detectability. Chemesthesis gauged with normosmics mirrored that with anosmics. Gas chromatography measurements showed that, even at 23 degrees C, the saturated vapor concentrations of the undetected stimuli, except vanillin, were well above the respective calculated nasal pungency threshold (NPT) from an equation that, in the past, had accurately described and predicted NPTs. We conclude that, except for octane and perhaps vanillin, the failure of the other four VOCs to precipitate nasal chemesthesis rests on a chemical-structural limitation, for example, the molecules lack a key property to fit a receptor pocket, rather than on a concentration limitation, for example, the vapor concentration is too low to reach a threshold value.

Odor detection of single chemicals and binary mixtures

The investigation explored the olfactory detectability of two chemically and structurally similar esters, ethyl propanoate and ethyl heptanoate, presented singly and in mixtures. Initially, we measured concentration-detection (i.e., psychometric) functions for the odor of ethyl propanoate and ethyl heptanoate presented singly. Using this information, we prepared binary mixtures of the two chemicals in varying complementary proportions and, also, selected concentrations of the single compounds, such that, if a rule of response-addition (i.e., independence of detection) were to hold, the stimuli (mixed and single) should approximate equal detection. Next, we measured the actual detectability of these stimuli within the same experiment. The results were analyzed in terms of response-addition (or -additivity) and of dose-addition (or -additivity). The outcome revealed that at low levels of detectability the mixtures approximate response-addition, that is, independence of detection, whereas at high levels of detectability they approximate dose-addition. In the light of previous findings for the olfactory detection of the more dissimilar chemical pairs 1-butanol/2-heptanone and butyl acetate/toluene, we conclude that the described outcome generalizes across a variety of chemical pairs.

Chemosensory additivity in trigeminal chemoreception as reflected by detection of mixtures

A series of experiments probed into the degree of chemosensory detection additivity exhibited by mixtures of ethyl propanoate and heptanoate in terms of their trigeminal detectability via nasal pungency (i.e., irritation) and eye irritation. Nasal pungency was tested in subjects lacking a functional sense of smell (i.e., anosmics) to avoid olfactory biases. First, we built concentration-detection functions for each chemical and sensory endpoint. Second, we used the data from the functions to prepare mixtures of the two compounds in complementary proportions, and suitable single-chemical standards, all of which should be equally detectable under a rule of complete additivity, i.e., independence of detection. Third, we compared the experimentally obtained detectability with that expected under such rule. The outcome revealed that, at a low detectability level (but still above chance), the mixtures showed complete additivity for both trigeminal endpoints. At a high detectability level (but below perfect detection), the mixtures showed complete additivity for nasal pungency but less than complete additivity for eye irritation. In the context of previous studies, the results consolidate a picture of higher degree of detection additivity at perithreshold levels in trigeminal than in olfactory chemoreception. The outcome presents another line of evidence suggesting broader chemical tuning in chemesthesis compared to olfaction.

Sensory and associated reactions to mineral dusts: sodium borate, calcium oxide, and calcium sulfate

Occupational exposure limits (OELs) for irritant dusts have had no quantifiable bases. This study (1) charted chemosensory feel, denoted chemesthesis here, to dusts of calcium oxide (1 to 5 mg/m(3)), sodium tetraborate pentahydrate [sodium borate] (5 to 40 mg/m(3)), and calcium sulfate (10 to 40 mg/m(3)); (2) examined correlates of the chemesthetic sensations; and (3) sought to illuminate the basis for potency. Twelve screened men exercised against a light load while they breathed air in a dome fed with controlled levels of dust for 20 min. Measured parameters included nasal resistance, nasal secretion, minute ventilation, heart rate, blood oxygenation, mucociliary transport time, and chemesthetic magnitude, calibrated to pungency of carbon dioxide. Subjects registered time-dependent feel from exposures principally in the nose, secondarily in the throat, and hardly in the eyes. Calcium oxide had the greatest potency, followed by sodium borate, with calcium sulfate a distant third. Of the physiological parameters, amount of secretion showed the best association with chemesthetic potency. That measure, as well as mucociliary transport time and minute ventilation, went into calculation of mass of dust dissolved into mucus. The calculations indicated that the two alkaline dusts increased in equal molar amounts with time. At equal molar concentrations, they had, to a first approximation, equal chemesthetic magnitude. On the basis of mass concentration in air or dissolved into mucus, calcium oxide and sodium borate differed in potency by a factor just above five, equal to the difference in their molecular weights. This relationship could inform the setting of OELs for a critical effect of irritation.

Detection of single and mixed VOCs by smell and by sensory irritation

We have measured complete concentration-detection (i.e., psychometric or detectability) functions to study the olfactory and ocular/nasal chemesthetic (a term that includes sensory irritation) impact of VOCs presented singly and in various binary mixtures. Such functions provide considerably more information than that provided by measuring only a "threshold". The outcome for single VOCs confirmed the much higher absolute sensitivity of olfaction compared to chemesthesis, but also demonstrated that the detection of ocular and nasal sensory irritation increases as a function of vapor concentration at a much higher rate than that for the detection of odor. The outcome for the binary mixtures revealed that, for both olfaction and chemesthesis, complete additivity of detection of individual components held at relatively low levels of detectability but broke down at higher levels. The breakdown for odor detection, compared to that for sensory irritation detection, was, first, more extensive, and, second, dependent to a larger extent on the degree of structural and chemical similarity/dissimilarity between the mixed VOCs.

PRACTICAL IMPLICATIONS

Concentration-detection functions for the chemesthetic and olfactory detectability of VOCs have shown that, even when nasal pungency and eye irritation begin to be evoked at concentrations orders of magnitude larger than those evoking odor, they sharply increase in detectability to become clearly noticeable. In contrast, odor detectability increases with concentration at a much lower rate. As a result, any fixed reduction (e.g., 10-times) in the concentration of a VOC will reduce detectability of sensory irritation much more dramatically than detectability of odor, within their respective ranges. Concentration-detection functions are particularly informative when employed to probe into the rules of dose- and response-additivity in mixtures. Our results for olfaction, and to a lesser extent for chemesthesis, indicate that additivity of detection of individual VOCs in mixtures is level-dependent: as detectability increases, the degree of additivity decreases. This suggests that a substantial improvement of perceived air quality could follow from control of just the few dominating chemosensory sources.

Reduced hospitalization cost for patients with pectus excavatum treated using minimally invasive surgery

BACKGROUND

Currently, few data exist regarding the relative costs associated with open and minimally invasive pectus excavatum repair. The aim of this study was to compare the surgical and hospitalization costs for these two surgical techniques and to identify factors responsible for cost differences.

METHODS

A retrospective review of hospital charts, patient and parent questionnaires, and hospital accounting records was performed for 68 patients who underwent surgical correction of pectus excavatum between June 1996 and December 1999.

RESULTS

In this series, 25 patients underwent open repair, whereas 43 patients underwent minimally invasive repair of pectus excavatum (MIRPE). The patient ages ranged from 4 to 19 years. The average ages for open repair (12 years) and MIRPE (11 years) did not differ significantly. As compared with open repair, MIRPE was associated with a 27% lower overall cost of hospitalization ( p < 0.05). The operating room costs were 12% higher for the patients who underwent MIRPE ( p < 0.05). The mean operative time for open repair was 3 h 15 min, whereas MIRPE required 1 h 10 min ( p < 0.001). The hospital stay for open repair averaged 4.4 days, as compared with 2.4 days for MIRPE ( p < 0.001). In contrast to other published series, the postoperative analgesia after MIRPE in this series consisted of narcotics, ketorolac, and methocarbamol. No patient received epidural analgesia, regardless of the repair technique selected. The postoperative complication rate was 4% in the open group and 14% in the MIRPE group. Most of the patients treated with either open or MIRPE reported postoperative oral narcotic usage for 2 weeks or less and returned to routine activities within 3 weeks. The patients and parents alike reported good to excellent overall outcomes in 85% or more of the open repair cases and 90% or more of the MIRPE cases.

CONCLUSIONS

These data demonstrate for the first time that the use of an alternate pain management strategy including, narcotics, NSAIDs, and methocarbamol, but without epidural catheters, results in reduced hospital length of stay and decreased overall hospitalization costs for MIRPE, as compared with open pectus repair. This cost benefit was achieved without compromising pain management or patient satisfaction with surgical care.

Draize rabbit eye test compatibility with eye irritation thresholds in humans: a quantitative structure-activity relationship analysis

Draize rabbit eye test scores, as modified maximum average score (MMAS), for 68 pure bulk liquids were adjusted by the liquid-saturated vapor pressure P. These 68 adjusted scores, as log (MMAS/P), were shown to be completely equivalent to eye irritation thresholds (EIT), expressed as log (1/EIT), for 23 compounds in humans. Thus, for the first time the Draize eye test in rabbits for pure bulk liquids is shown to be perfectly compatible with eye irritation thresholds in humans. The total data set for 91 compounds was analyzed by the general solvation equation of Abraham. Values of log (MMAS/P) or log (1/EIT) could be fitted to a five-parameter equation with R2 = 0.936, SD = 0.433, AD = 0.000, and AAD = 0.340 over a range of 9.6 log units. When divided into a training set of 45 compounds, the corresponding equation could be used to predict the remaining 46 compounds in a test set with AD = -0.037 and AAD = 0.345 log units. Thus, the 91-compound equation can now be used to predict further EIT values to around 0.4 log units. It is suggested that the mechanism of action in the Draize test and in the human EIT involves passive transfer of the compound to a biophase that is quite polar, is a strong hydrogen bond base, a moderate hydrogen bond acid, and quite hydrophobic. The biophase does not resemble water or plasma, but resembles an organic solvent such as N-methylformamide.

Quantification of chemical vapors in chemosensory research

Studies of olfaction and chemesthesis often rely on nominal, liquid-phase dilutions to quantify the chemicals tested, even though the associated vapor concentrations constitute the actual stimuli. For more than a decade now, our systematic studies of the olfactory and chemesthetic potency of members of homologous chemical series have routinely included quantification of vapors via gas chromatography. This article depicts the relationships between liquid- and vapor-phase concentrations for 60 volatile organic compounds and summarizes the theoretical and technical factors influencing these relationships. The data presented will allow other investigators working with these materials to express them as vapor concentrations even when they lack the resources to perform the analytical measurements. The paper represents a step toward creation of a practical archive for vapor quantification in chemosensory science.

Dose-addition of individual odorants in the odor detection of binary mixtures

In a series of experiments, we have explored the rules of olfactory detection agonism between the odorants butyl acetate and toluene. First, we obtained the concentration-detection function for the odor of the individual compounds. Second, we selected the concentrations of the two substances producing three levels of detectability (low, medium, and high) and, for each level, tested the comparative detectability of the two single chemicals and three mixtures of varying proportions. In each case, the mixtures were prepared in such a way that, if a rule of complete dose addition were to hold, all five stimuli (two single, three mixtures) should be equally detected. The outcome revealed complete dose addition at relatively low detectability levels but fell short of dose addition at medium and high levels. A recent analogous study on trigeminal chemosensory detection via nasal pungency and eye irritation of these same stimuli have shown a similar trend but showed a less dramatic loss of dose additivity with increased detectability. These results on detection of mixtures suggest a more selective window of chemical tuning (i.e. less dose addition) in olfaction than in trigeminal chemoreception.

Implicit and explicit memory for odors: hemispheric differences

In two experiments, implicit and explicit tests were used to investigate the lateralization of odor memory. Odors were at all times presented monorhinically. At test, odors were presented to either the ipsi- or the contralateral side of the nostril used for inspection. In Experiment 1, participants were first primed to a set of odors. At test, response latencies for odor identification were measured. The results were that priming odors tested via the left but not the right nostril were identified faster than control odors. In Experiment 2, a similar design probed episodic recognition memory. Memory performance did not differ between the left and right nostrils, but the measures of response latency favored the right side. The study demonstrates that it is possible to tap differences in memory performance between the cerebral hemispheres through monorhinic presentation of odors in healthy persons, and that these differences depend on the test nostril rather than the inspection nostril.

Improving the health of workers in indoor environments: priority research needs for a national occupational research agenda

Indoor nonindustrial work environments were designated a priority research area through the nationwide stakeholder process that created the National Occupational Research Agenda. A multidisciplinary research team used member consensus and quantitative estimates, with extensive external review, to develop a specific research agenda. The team outlined the following priority research topics: building-influenced communicable respiratory infections, building-related asthma/allergic diseases, and nonspecific building-related symptoms; indoor environmental science; and methods for increasing implementation of healthful building practices. Available data suggest that improving building environments may result in health benefits for more than 15 million of the 89 million US indoor workers, with estimated economic benefits of $5 to $75 billion annually. Research on these topics, requiring new collaborations and resources, offers enormous potential health and economic returns.

Sensory detection of glutaraldehyde in drinking water-emergence of sensitivity and specific anosmia

A study of 30 young adults (15 males, 15 females), screened to have normal olfaction, measured detection of the flavor of glutaraldehyde, a biocide that could occur in disinfected potable water. Over the range of interest, up to 100 p.p.m., flavor derived from olfactory stimulation. Higher concentrations would cause oral irritation. Fourteen subjects failed to detect the glutaraldehyde in the first of four sessions of testing. Eight of the 14 (seven males, one female) continued to exhibit the anosmia throughout testing. The other six (one male, five females) began to detect the material in session two and exhibited increasing sensitivity over sessions two to four. Their average sensitivity never reached that of the 16 subjects who evinced no anosmia and who also improved their performance over sessions. The combined group of 22 could detect 17 p.p.m. Less thorough testing would have yielded much higher values. Specific anosmia for this dialdehyde has precedence in anosmia for various monoaldehydes, most notably isobutyraldehyde. The positive influence of experience with a material on detection has been found previously, most intriguingly by Wysocki and colleagues, who showed that experience could differentially induce sensitivity to the odorant androstenone and suggested that the phenomenon might occur for other compounds. Glutaraldehyde appears to be one, perhaps of many.

A model for odour thresholds

Odour detection thresholds, that we have previously obtained, have been analysed by a general equation for selective transport. It is shown that such selective transport can account for some 77% of the total effect. The remainder is due to a specific size effect, that might involve odour-binding proteins, and a specific effect for aldehydes and carboxylic acids. Our analysis raises the question of whether selective transport is physically separable from the specific effects of receptor activation. The model predicts a chemical cut-off in odour detection along any homologous series.

Psychometric functions for the olfactory and trigeminal detectability of butyl acetate and toluene

We measured psychometric (i.e. concentration-response) functions for the detection of odor, nasal pungency and eye irritation from butyl acetate and toluene. Olfactory detection was measured in subjects with normal olfaction (i.e. normosmics) for whom nasal trigeminal detection does not interfere because it requires much higher concentrations. Nasal trigeminal detection, called nasal pungency, was measured only in subjects lacking olfaction (i.e. anosmics) in order to avoid odor interference. Ocular trigeminal detection, called eye irritation, was measured in both groups. The method employed entailed a two-alternative, forced-choice procedure with presentation of increasing concentrations. The outcome showed, for both chemicals, similar ocular trigeminal chemosensitivity in normosmics and anosmics and similar overall ocular and nasal trigeminal chemosensitivity. Olfactory sensitivity was much higher than both forms of trigeminal sensitivity by concentration differences of six and four orders of magnitude for butyl acetate and toluene, respectively. Detectability plots (i.e. detection performance vs log concentration) for the three sensory endpoints followed an S-shaped function with a middle range section that showed a robust linear fit (r > 0.94) on graphs of z-score vs log concentration. These detectability functions allow the calculation of olfactory and trigeminal thresholds at various levels of performance. At a point half-way between random and perfect detection, trigeminal and olfactory threshold concentrations were, respectively, 0.67 (+/-0.32) and 2.28 (+/-1.77) log units lower than those measured by us in the past for the same chemicals using an analogous procedure but under just one, fixed, level of performance. The available data suggest that, although considerably laborious, detectability functions provide chemosensory thresholds of closer relevance to environmentally realistic conditions (e.g. whole-body exposures).

Ocular and nasal trigeminal detection of butyl acetate and toluene presented singly and in mixtures

To probe into the rules of trigeminal chemosensory agonism in a binary mixture of chemicals we measured, first, the detectability (i.e., psychometric) function for eye irritation and for nasal pungency of butyl acetate and toluene, singly. (To avoid olfactory biases, nasal pungency was measured in a group of anosmics, i.e., persons lacking a functional sense of smell.) Then, based on the detectability function obtained for the individual chemicals, we prepared mixtures where the 2 components varied in their relative proportions but, if a simple rule of complete sensory agonism (in the sense of dose-additivity) were to hold, the mixtures should be as detectable as the reference concentration of each of the single chemicals. For both trigeminal endpoints (i.e., eye irritation and nasal pungency), the results showed that stimuli of relatively low detectability did show complete sensory agonism, whereas stimuli of relatively high detectability fell short of complete sensory agonism when compared with the detectability of the single substances. Further testing of additional binary and higher order mixtures will confirm whether or not a structure-activity model of trigeminal chemosensory impact of single chemicals, based on selected physicochemical parameters of the stimuli, can also be applied to chemical mixtures.

Orbital response indicates nasal pungency: analysis of biomechanical strain on the skin

Stimulation of the human nasal passage with pungent vapor elicits motor responses in a zone around the eye. This investigation addressed whether quantification of such responses, particularly activity of the orbicularis oculi muscle, could yield a sensitive index of nasal pungency. We placed an array of small, high-contrast targets just beneath the lower eyelid and videotaped their movement to capture deformation of the skin atop the orbicularis oculi during 3 s stimulation with pungent concentrations of ethyl acetate. Eleven subjects participated. Analysis of the movements served to determine mechanical strain, which yielded a single index that we termed 'maximum strain'. This increased with concentration of the vapor and with time during and just after stimulation. Comparison with psychophysical data showed that the strain became evident at concentrations just detectable as pungent. Maximum strain measured on the skin shows promise as an objective index of pungency.

Human breathing and eye blink rate responses to airborne chemicals

Increased levels of air pollution have been linked with morbidity and mortality, but mechanisms linking physiologic responses to quality of life and productivity issues remain largely unknown. Individuals often report irritation of the nose and/or eyes upon exposures to environmental contaminants. Evaluation of these self-reports would be greatly aided by the development of valid physiological markers. Chamber studies (unencumbered exposures) of nonsmoker responses to environmental tobacco smoke offer two candidate end points: (a) Tidal volume increases and breathing frequency declines with stimuli that elicit only moderate irritation. (b) Eye blink rate increases only with a concentration sufficiently high to cause progressive worsening of eye irritation with prolonged exposure. Experiments with very brief nasal-only presentations also suggest the value of breathing changes as sensitive markers of irritation: (a) Tidal volume is inversely related to perceived nasal irritation (NI) intensity in both normal and anosmic (lacking olfactory input) individuals, although normals exhibit greater NI sensitivity. (b) Inhalation duration, in both groups, declines only with trigeminal activation sufficient to cause readily perceptible NI in anosmics. Changes in eye blink rate and breathing may be useful in the investigation of irritation and other effects of air pollution, and could be quite useful in investigations of mixtures of volatile organic compounds.

Psychometrics of odor quality discrimination: method for threshold determination

There is no natural physical continuum for odor quality along which an odor quality discrimination (OQD) threshold can be measured. In an attempt to overcome this problem, the substitution-reciprocity (SURE) method defines a framework for the measurement of an OQD threshold. More specifically, it (i) defines a threshold concept for OQD, including the quantification of qualitative change of the stimulus, and (ii) suggests how to avoid perceived intensity as an unwanted cue for discrimination. In doing this, the psychometric properties of odor quality in the case of eugenol and citral are investigated using both discrimination (experiment 1) and scaling (experiment 2). Based on discriminatory responses, a change of approximately one-third in stimulus content was needed to reach the OQD threshold for eugenol and citral.

Connection between chromatographic data and biological data

There are no previous references to the direct use of GLC data in the correlation of biological processes, but we show that GLC retention data can be used in the correlation of several such processes involving gaseous solutes. There are a number of reports of RP-HPLC and MEKC data being used in the correlation of biological processes, but they are mostly restricted as to the number and type of solute studied. We show that if chromatographic data are used to obtain solvation descriptors for solutes, and if these descriptors are then used in the correlation of biological processes, that this indirect connection is a much more powerful and generally applicable method than is the direct connection between chromatographic data and biological data.

Quantification of odor quality

The relationship between odor quality and molecular properties is arguably the most important issue in olfaction. Despite sophistication in the chemical characterization of molecules, accompanying perceptual characterization has had little quantitative usefulness, relying mostly on enumerative description. As a result of weak interest in the topic outside industry and little agreement regarding how to measure quality, the field of olfactory psychophysics has failed to develop a substantial database for odor quality and has offered little help to other researchers, e.g. neurobiologists, in choice of stimuli, interpretation of outcome or testable hypotheses. This review scrutinizes how psychophysicists and others have measured quality and offers criteria for useful techniques. Most measures have had a subjective component that makes them anachronistic with modern methodology in experimental behavioral science, indeterminate regarding the extent of individual differences, unusable with infrahumans and of unproved ability to discern small differences. Techniques based upon performance, rather than on the more common reporting of mental content, offer firmer possibilities for growth. These techniques inevitably tap the discriminative basis of perception. The nonsubjective techniques have high sensitivity, can have counterparts in infrahuman research, are suitable to examine individual differences and yield non-negotiable answers with potential archival value. Discriminative techniques have their limitations, too-principally excess sensitivity that abridges their use to comparisons between similar-smelling stimuli. Research has begun to extend that range and may overcome the limitation. Application of discriminative methods may have the side-effect of shifting focus in structure-activity research from searches for molecular least common denominators that underlie often vague similarity to the search for molecular properties of importance in discrimination of small differences.

Comparison of two stimulus-delivery systems for measurement of nasal pungency thresholds

Using representative members of each of three homologous series of chemicals-ketones, acetates and alcohols-we measured nasal pungency thresholds in anosmics via two stimulus-delivery systems. The first system consists of the fairly commonly used 270 ml, plastic 'squeeze bottles'. The second system consists of 1900 ml, glass vessels with Teflon tubing and nose-pieces. Although bulkier and more susceptible to mechanical breakage, the glass vessels possess advantages that can allow them to provide 'environmentally realistic' chemosensory thresholds, i.e. thresholds closer in absolute values to those that might be obtained under whole-body exposures. Such advantages include a larger volume of the vapor-source to accommodate whole sniffs, and a tight nose-nose-piece connection to avoid stimulus dilution. The outcome revealed that, for every chemical, the glass vessels provided nasal pungency thresholds significantly lower than those provided by the squeeze bottles. The difference amounted, on average, to a factor of 4.6, though the relative potency of the compounds remained the same under both systems. Additionally, when tested with the highest homologues used here, namely, octyl acetate and 1-octanol, anosmics using the glass vessels had little or no difficulty achieving the criterion for threshold whereas they did have difficulty when using the squeeze bottles.

Latency and accuracy of discriminations of odor quality between binary mixtures and their components

Subjects made timed, same-different discriminations of odor quality, with the following principal findings: (i) latency reflected accuracy, with difficult discriminations, i.e. those between 50-50 mixtures and their components, requiring more time than less difficult discriminations, i.e. those between unmixed chemicals. This finding demonstrated the face validity of latency as a measure of qualitative similarity. (ii) Latency provided better resolution among pairs of odors than did errors of discrimination. This finding demonstrated the utility of collecting response times. (iii) Latency-based similarities among odors tested previously predicted similarities among pairs not yet tested. This finding demonstrated internal/predictive validity. (iv) A signal detection model assuming a differencing strategy best described the pattern of errors. Subjects appeared to make relative judgements regarding quality. (v) Finally, latency-based similarities between mixtures and their components demonstrated additivity. This finding suggested that binary mixtures fall on straight lines connecting their components in 'odor-space'.

Measurement of sensitivity to olfactory flavor: application in a study of aging and dentures

Olfaction involves a dual sensory process for perceiving odors orthonasally (through the nostrils) and retronasally (through the mouth). This investigation entailed developing a measure of sensitivity to an odor delivered in an orally sampled food (orange flavoring in a sucrose-sweetened gelatin) and examining sensitivity in the elderly. In experiment 1, olfactory flavor sensitivity was 49 times lower in elderly (n = 21) than in young (n = 28) subjects. In experiment 2, with 73 elderly women, higher olfactory flavor sensitivity correlated significantly with higher orthonasal perception (Connecticut Chemosensory Clinical Research Center test). Some women, however, exhibited low olfactory flavor sensitivity despite high orthonasal perception; none had high olfactory flavor sensitivity and low orthonasal perception. Those who wore complete or palatal covering dentures had lower olfactory flavor sensitivity than those who were dentate or wore dentures that did not cover the palate. Through multiple regression analysis, orthonasal perception and denture status were found to be independent contributors to predicting olfactory flavor sensitivity. In summary, elderly subjects showed depressed olfactory flavor sensitivity (i.e. retronasal sensitivity) that related to poor orthonasal olfactory perception and denture characteristic. Thus, while good orthonasal olfaction may be necessary for good olfactory flavor sensitivity, it is not sufficient. Other factors, some associated with oral conditions, may impede release and retronasal transport of odors from the mouth to the olfactory receptors.

Chemosensory detectability of 1-butanol and 2-heptanone singly and in binary mixtures

Using 1-butanol and 2-heptanone as stimuli, we measured detectability (i.e., psychometric) functions for the odor, nasal pungency, and eye irritation of these two substances alone and in binary mixtures. Nasal pungency responses were tested in subjects lacking olfaction (i.e., anosmics) for whom odors do not interfere. Eye irritation responses were tested in normosmics and anosmics, and found to be similar in both groups so their results were pooled. When all stimuli--single and mixtures--were transformed into concentration units of one (or the other) chemical, a single function could fit all data from the same sensory end point with a correlation coefficient of 0.91 or higher. The outcome lends support, as a first approximation, to the notion of chemosensory agonism, in the sense of dose additivity, between the members of binary mixtures presented at perithreshold levels.

Gastrointestinal autonomic nerve tumors in the pediatric population: a report of four cases and a review of the literature

BACKGROUND

Gastrointestinal autonomic nerve tumors (GANTs) are a subpopulation of gastrointestinal stromal tumors (GISTs) that are characterized by ultrastructural features resembling enteric autonomic nerve cells, without epithelial, Schwannian, or smooth muscle differentiation. Delineation of the clinicopathologic features of GANT in the pediatric population is lacking.

METHODS

The clinicopathologic and outcome data for four pediatric patients with GANT are presented. The data from these patients and four previously reported pediatric patients are summarized and compared with data for GANT in adults.

RESULTS

All four cases occurred in females at a mean age of 12.5 years. The primary tumor site was the stomach in all cases, and the mean tumor size was 6.3 cm. Immunocytochemical and ultrastructural examination were essential in distinguishing GANT from GIST in all cases by identifying features of neural origin (neuron specific enolase in all four cases, NFP in three cases, S-100 in two cases, dense core neurosecretory granules in all four cases, and neuritelike processes in all four cases), while failing to identify features of myogenic origin (no desmin, smooth muscle actin, myofilaments, or dense bodies were found in any of the cases). Primary treatment was surgical, with chemotherapy administered to 1 patient at the time of recurrence. All patients are alive after a mean follow-up of 60 months (range, 8 months to 9 years).

CONCLUSIONS

Similarities of pediatric GANT to GANT in adults include the need for a high index of suspicion for diagnosis; comparable histopathologic, immunohistochemical, and ultrastructural features; and surgery as the primary therapy. Distinguishing features in children may be a prevalence among females in the second decade, a predominance of smaller gastric tumors, and a positive prognostic value of younger age.

Gastrointestinal autonomic nerve tumors in the pediatric population: a report of four cases and a review of the literature

BACKGROUND

Gastrointestinal autonomic nerve tumors (GANTs) are a subpopulation of gastrointestinal stromal tumors (GISTs) that are characterized by ultrastructural features resembling enteric autonomic nerve cells, without epithelial, Schwannian, or smooth muscle differentiation. Delineation of the clinicopathologic features of GANT in the pediatric population is lacking.

METHODS

The clinicopathologic and outcome data for four pediatric patients with GANT are presented. The data from these patients and four previously reported pediatric patients are summarized and compared with data for GANT in adults.

RESULTS

All four cases occurred in females at a mean age of 12.5 years. The primary tumor site was the stomach in all cases, and the mean tumor size was 6.3 cm. Immunocytochemical and ultrastructural examination were essential in distinguishing GANT from GIST in all cases by identifying features of neural origin (neuron specific enolase in all four cases, NFP in three cases, S-100 in two cases, dense core neurosecretory granules in all four cases, and neuritelike processes in all four cases), while failing to identify features of myogenic origin (no desmin, smooth muscle actin, myofilaments, or dense bodies were found in any of the cases). Primary treatment was surgical, with chemotherapy administered to 1 patient at the time of recurrence. All patients are alive after a mean follow-up of 60 months (range, 8 months to 9 years).

CONCLUSIONS

Similarities of pediatric GANT to GANT in adults include the need for a high index of suspicion for diagnosis; comparable histopathologic, immunohistochemical, and ultrastructural features; and surgery as the primary therapy. Distinguishing features in children may be a prevalence among females in the second decade, a predominance of smaller gastric tumors, and a positive prognostic value of younger age.

Sensory properties of selected terpenes. Thresholds for odor, nasal pungency, nasal localization, and eye irritation

We tested four normosmics and four anosmics in detection thresholds for six terpenes commonly found indoors: cumene, p-cymene, delta-3-carene, linalool, 1,8-cineole and geraniol. Normosmics provided odor thresholds and anosmics provided nasal pungency thresholds. All subjects provided nasal localization (i.e., right/left nostril) and eye irritation thresholds. Each type of threshold was measured eight times per subject-stimulus combination. Stimuli were presented from squeeze bottles in a two-alternative forced-choice procedure via an ascending method of limits. Odor thresholds ranged between 0.1 and 1.0 parts per million (ppm, by volume). Nasal pungency thresholds lay about three orders of magnitude above odor thresholds. Nasal localization and eye irritation thresholds did not differ between normosmics and anosmics, and fell close to nasal pungency thresholds. Olfactory thresholds could be obtained for all stimuli in all repetitions using the criterion of five correct choices in a row. Trigeminal thresholds (i.e., pungency, localization and eye irritation) could be obtained on all repetitions only for some terpenes using that same criterion. Carene and cineol produced nasal pungency and eye irritation on all repetitions. None of the terpenes could be localized on all repetitions, but cineol was localized a higher percentage of instances than were the other stimuli. At the other extreme, geraniol failed to evoke any of the three trigeminal responses in most instances. Overall, the results indicate that the three trigeminal thresholds produce a uniform view of the potency of these terpenes, with nasal pungency and eye irritation being slightly more sensitive than nasal localization. Furthermore, application of a previously derived linear solvation energy relationship to the results reinforced the view that physicochemical properties can predict the chemesthetic impact of volatile organic compounds.

Draize eye scores and eye irritation thresholds in man can be combined into one QSAR

Draize eye scores (DES) of 37 pure organic liquids have been converted into scores for the corresponding vapors, DES/P0, where P0 is the liquid vapor pressure in atmospheres at 298 K. It is shown that there is a constant difference of 6.7 between values of log(DES/P0) and log (1/EIT), where EIT is the eye irritation threshold in parts per million (ppm, by volume) of eight vapors for human subjects. The 37 log(DES/P0) values can be combined with log(1/EIT) values for 17 vapors into one quantitative structure-activity relationship (QSAR) for sensory potency (SP) using our general solvation equation, [formula: see text] where R2 is an excess molar refraction, pi 2H is the compound polarizability/dipolarity, sigma alpha 2H and sigma beta 2H are the compound hydrogen-bond acidity and basicity, and L16 is the gas-hexadecane partition coefficient at 298 K. n is the number of data points, r the correlation coefficient, SD the standard deviation, and F the F-statistic. LogSP is then either [log(DES/P0) - 0.66] or log (1/EIT), confirming the result for the eight common compounds. It is suggested that the equation can be used to predict eye irritancy of organic vapors and pure liquids. It is further suggested that for the compounds in the data set, the main process in eye irritation is transfer of the compound from the vapor or pure liquid to a biological phase, and a number of chemical properties of the biological phase have been mapped out through the equation. These properties are consistent with corresponding properties for a number of organic liquid phases.